How to properly apply PBR displacement on non rectangular Planes?
hope i understand your request. you need a non rectangular plane to be displaced, right? I think best way should be insert a plane, subdivide it, select and remove not necessary vertex.


Then add the modifiers you need. in the image you can see a displace modifier with cloud texture and subsurf added.

Them you can unwrap (you can do that in ortho top view and then uv -&gt; project from view) and apply the shaders.

It was that you need?